Intraocular lenses and methods for making same

ABSTRACT

New intraocular lenses and methods for producing such lenses are disclosed. In one embodiment, the intraocular lens comprises an optic; and at least one fixation member, e.g., haptic, secured to and extending from the optic, the fixation member being made from a compressed item having a compressed thickness and comprising of a polymer selected from the group consisting of methyl methacrylate homopolymers, methyl methacrylate-containing copolymers and mixtures thereof, the compressed item being derived by subjecting an item having a thickness to compression, preferably along an axis substantially parallel to the thickness, to reduce the thickness, provided that the compressed item has increased tensile strength relative to the item and is substantially no less intraocular lens manufacturable than is the item.

This application is a continuation of application Ser. No. 08/315,736,filed Sep. 30, 1994, abandoned which, in turn, is a continuation ofapplication Ser. No. 08/126,728 filed Sep. 24, 1993 abandoned, which, inturn, is a continuation of application Ser. No. 07/933,410 filed Aug.21, 1992, abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to intraocular lenses and to methods formaking such lenses. More particularly, the present invention relates tointraocular lenses having one or more enhanced physical properties, forexample, tensile strength and/or flexibility, which benefit the lenses.

The use of intraocular lenses (IOLs) to improve vision and/or to replacedamaged or diseased natural lenses in human eyes, particularly naturallenses impaired by cataracts, has achieved wide acceptance. Accordingly,a variety of IOLs has been developed for surgical implantation in theposterior or anterior chambers of the eye according to a patient'sneeds.

Known IOLs comprise an optical lens portion or optic which includes anoptical zone, and one or more, preferably two, supporting structures,called fixation members or haptics, which are secured to and extend fromthe optic and are for contacting eye tissue to fix or hold the IOL inthe proper position after implantation. The optic and the fixationmember or members may each comprise a material such as a homopolymer ofmethyl methacrylate or polymethylmethacrylate (PMMA) or a copolymercontaining methyl methacrylate. The entire IOL, that is the optic andthe fixation member or members, may be made of a single piece or item ofmaterial, for example, PMMA.

In order to obtain a high degree of performance, the IOL should be madeof a material or materials which have good physical or mechanicalproperties. For example, the fixation member or members should havesufficient tensile strength, flexibility and fatigue resistance so asnot to break or separate from the optic during IOL implantation and tobe effective in long term use in the eye. Certain materials, inparticular, the methyl methacrylate-containing polymers noted above,have certain properties, such as optical clarity and biocompatibility,which make them very useful in IOLs. However, it would be advantageousto enhance certain other physical properties, as noted above, of suchmaterials to further benefit IOLs made at least in part from suchmaterials. This physical property enhancement would be all the morebeneficial if it could be accomplished without the need for anysubstantial or significant change or changes (other than the enhancementitself) in the manner in which IOLs are produced.

European Patent Publication No. 0438043A2 discloses IOLs made from PMMAwhich is subjected to stretching along at least two mutually angulatedaxes to increase the material's dimension along the axes of stretch by20% to 65%, preferably by 40%, thereby providing increased tensilestrength and flexibility. Several disadvantages are apparent with such a"multi-axial" stretching system. For example, the material may not beuniformly stretched, which can cause distortions and otherirregularities in the material and the final IOL product. In addition,because a relatively complex and cumbersome clamping/stretching systemis employed, a relatively high percentage of the stretched material mustbe discarded. Further, the amount or degree of stretching is quite high,apparently because of the relative inefficiency of the "multi-axial"stretching technique in providing improved mechanical properties.Materials which are highly stretched have a tendency to be moredifficult, relative to unstretched materials, to manufacture, forexample, machine, into IOLs.

Kataoka U.S. Pat. No. 4,550,057 discloses compressing PMMA sheets toreduce the thickness of the sheet by a factor of at least 3 and increaseimpact resistance by a factor of at least 10. Large compression forcesand/or temperatures on the order of 130° C. to 160° C. are employed toachieve this large degree of compression. These compressed sheets aresuitable as a glazing material for windows for vehicles and buildings.This patent does not in any way disclose or suggest anything about IOLsor making IOLs.

Fortin U.S. Pat. No. 3,632,841 discloses compression stretching largeacrylic sheets at temperatures of 250° F. and above between polished,heated and lubricated plates to form compressed sheets which are aboutone-third as thick as the original sheets. This patent discloses thatsuch compression stretching provides improved physical and opticalproperties. This patent does not in any way disclose or suggest anythingabout IOLs or making IOLs.

Franz et al U.S. Pat. No. 4,454,203 discloses coating an acrylicsubstrate with a compatible polymeric film which is less extensible thanthe substrate and pressing the coated article to reduce thickness sothat the compressed article has a thickness of about one-third that ofthe original article. Reduced amounts of compressive force areapparently required to achieve this large reduction in thickness, andthe resulting plastic article is said to have improved optical quality.This patent does not in any way disclose or suggest anything about IOLsor making IOLs.

There continues to be a need for IOLs having enhanced properties and formethods for making such IOLs.

SUMMARY OF THE INVENTION

New IOLs and methods for producing IOLs have been discovered. Thepresent IOLs are derived from materials containing methylmethacrylate-containing polymers which have been subjected to controlledand limited compression to enhance one or more physical properties ofthe materials and the resulting IOLs. It has been found that meaningfulphysical property enhancement can be achieved without substantiallyinterfering with the overall IOL manufacturing process. For example, thelimited compression to which the materials are subjected in accordancewith the present invention provide enhanced tensile strength,flexibility and/or fatigue resistance, without forming a material whichis substantially more difficult to manufacture into an IOL. Thus, afterbeing compressed, the "compressed" material may be processed, forexample, in accordance with conventional IOL manufacturing procedures,to obtain an IOL having advantageously enhanced physical properties.Because the present compression processing involves a more uniformapplication of force without clamping the material being processed, lessmaterial is wasted and/or a more uniform IOL is produced, for example,relative to the "multi-axial" stretching process of the prior art.

In one broad aspect, the present invention involves IOLs which comprisean optic and at least one fixation member which is secured to andextends from the optic. The fixation member or members, and preferablythe optic as well, are made from a compressed item having a compressedthickness and comprising a polymer selected from methyl methacrylatehomopolymers, methyl methacrylate-containing copolymers and mixturesthereof. The compressed item is derived by subjecting an item tocompression, preferably along an axis substantially parallel to thethickness of the item, to reduce this thickness. The tensile strength ofthe compressed item is increased relative to the tensile strength of theitem prior to being compressed. In one embodiment, the compression ispreferably controlled so that the compressed item is substantially noless IOL manufacturable than the original, uncompressed item. That is,the compressed item can preferably be manufactured into an IOLsubstantially as easily, for example, using substantially no moreenergy, time, cost and/or effort, as can the original, uncompressed itembe manufactured into an IOL.

In a particularly useful embodiment, the thickness of the uncompresseditem is reduced by 30% or less as a result of the compression. In otherwords, the compressed thickness of the compressed item is equal to 70%or more of the thickness of the original, uncompressed item. Thisfeature, which is one indication of the controlled or limited amount ofcompression involved in the present invention, provides meaningfulenhancements in one or more of the physical properties of the item, andthe IOL derived therefrom, and clearly distinguishes the presentinvention from the prior art. Thus, previous compression processing ofPMMA and similar materials have involved substantially greater thicknessreductions. The present invention is based, in part, on the discoverythat sufficient enhancements in material physical properties can beachieved to benefit IOLs with a controlled or limited amount ofcompression. An additional benefit of this controlled, limited amount ofcompression is that the compressed material is substantially free ofdistortions and non-uniformities which become more prevalent as thedegree of compression or stretching to which an item is subjected isincreased.

In a further embodiment, the item is preferably subjected to compressionat a temperature in the range of about 80° C. to about 130° C., morepreferably about 80° C. to about 125° C. These relatively mildtemperatures are consistent or in line with the controlled or limiteddegree of compression to which the item is subjected in accordance withthe present invention. The mild temperatures noted herein reduce theamount of time involved in processing, for example, in heating andcooling, the material in accordance with the present invention. Inaddition, these mild temperatures reduce, or even eliminate, anydistortions or non-uniformities which can result in processing thepresent materials at higher temperatures where the materials are moreflowable and subject to change. Further, such mild temperatures reduce,or even eliminate, depolymerization of the present materials so thatlonger polymer chains are maintained and compressed materials having oneor more superior physical properties are obtained, relative toprocessing at higher temperatures.

In one embodiment, only the fixation member or members of the IOL areproduced from a compressed item in accordance with the presentinvention. Alternately, the optic and fixation member or members of theIOL are produced from the compressed item of material. In a usefulembodiment, a single IOL is formed from the compressed item. Thisfeature again distinguishes the present invention from the prior artwhich discloses stretching or compressing large sheets of PMMA and thelike materials. However, it should be noted that two, three, four ormore IOLs can be produced from a single compressed item.

In another aspect of the present invention, methods for making IOLs areprovided. These methods comprise compressing an item having a thickness,preferably along an axis substantially parallel to the thickness, toreduce the thickness and form a compressed item. The item comprises apolymer selected from methyl methacrylate homopolymers, methylmethacrylate-containing copolymers and mixtures thereof. This compresseditem has increased tensile strength relative to the original,uncompressed item. An IOL is formed from the compressed item andincludes an optic and at least one fixation member secured to the opticand extending from the optic. In a particularly useful embodiment, theforming step includes machining the compressed item and the compressingoccurs at conditions such that the machining is substantially no moredifficult, for example, relative to substantially identically machiningthe original, uncompressed item.

The present IOLs have enhanced physical properties which reduce the riskof disassembly or degradation during installation or long term use inthe eye. Such physical property enhancement is achieved with little orno detriment, for example, to the conventional IOL manufacturingprocess. Further, the present methods for producing IOLs involvecontrolled or limited amounts of compression so as to reduce, and evenminimize, material waste, energy and processing inefficiencies, anddistortions and non-uniformities in the final IOL products. The presentinvention very efficiently and effectively provides IOLs which haveenhanced physical properties and are advantageously useful and durable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a typical IOL including optic and fixationmembers made of a material embodying principles of the presentinvention.

FIG. 2 is a side view of the lens of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Many different IOL configurations and sizes may be employed in thepresent invention. To illustrate, a typical IOL is shown generally at 10in FIG. 1, and includes an optic 11 suitably shaped for proper focusingand having integrally formed fixation members or haptics 12 and 14extending therefrom. IOL 10 may be plano-convex, as shown, or bi-convex,concavo-convex or any other optical configuration as desired. The opticmay also have refractive and diffractive optic portions, severalrefractive curves or an aspheric surface to give bifocal or multifocalcapabilities and be formed of a material having different optical orphysical properties than the material forming haptics 12 and 14. Anyhaptic shape, configuration, or number may be utilized in accordancewith the teachings of the present invention. Small apertures, notchesand the like may be provided in the optic 11, for example, adjacent theconnection with haptics 12 and 14, respectively, for reception ofimplantation tools.

In lenses of this type, the central portion or optic is a solid body,for example, about 5 mm to about 8 mm in diameter, with the very smallcross section fixation members or haptics extending outwardly to createan overall size, between the free ends of the haptics, in the range ofabout 9 mm to about 14 mm. Any forces exerted on the haptics, forexample, during installation or implantation of the IOL, or during useof the IOL, create high stress at the junction between the haptics andthe optic. It is thus advantageous that the fixation member or membershave high tensile strength, flexibility and fatigue resistance.

The items, for example, cores, buttons and the like, employed inaccordance with the present invention comprise materials selected frommethyl methacrylate homopolyers, co-polymers of methyl methacrylate andone or more other monomers, such as butyl acrylate, ethyl acrylate,lauryl acrylate and the like. In addition, the presently useful methylmethacrylate-containing copolymers can include polymerizable ultraviolet(UV) light absorbers, for example, present in the range of about 0.01%to about 2% by weight of the copolymer, effective to provide the desireddegree of UV absorbance to the final IOL product. Examples of such UVabsorbing monomers include functionalized benzophenones, functionalizedbenzotriazoles and the like. The presently useful items may include aneffective amount of one or more other components to provide or enhanceone or more properties which are beneficial in making the IOL and/or inthe final IOL itself. For example, a UV absorbing additive (notpolymerized) may be included or physically mixed into the item.

The methyl methacrylate homopolymers and/or methylmethacrylate-containing copolymers preferably comprise a major amount,i.e., at least about 50% by weight, and more preferably at least about80% or about 90% by weight, of the item to be processed in accordancewith the present invention. The optic of the final IOLs, and preferablythe compressed items, are optically clear.

In order to provide a blank from which an IOL is to be formed inaccordance with the present invention, an item, for example, a core, ofuncompressed material is provided. This item, while it is uncompressed,includes a polymeric material which is fully polymerized. Thus, theprocessing, e.g., compressing, in accordance with the present invention,preferably results in substantially no additional polymerization orcuring of this polymeric material.

Any suitable system and equipment may be employed to provide thecompressed items and form IOLs from such compressed items in accordancewith the present invention. Thus, the specific system and equipmentemployed is not critical and, for example, may be selected from systemsand equipment which are conventionally employed to compress PMMA-typematerials and to form IOLs from PMMA-type materials. The systems andequipment described herein are illustrative of the systems and equipmentwhich may be employed.

In accordance with one embodiment, the uncompressed core, which istransparent and colorless and is made of, for example, PMMA, is placedon the platen of a press or similar device suitable for applying acompressive force to the core between two heating plates so that thethickness of the core is located between the plates and separates theplates. The heating plates are energized so as to heat the core to atemperature above about 30° C., preferably between about 80° C. to about130° C. and more preferably between about 80° to about 125° C. After thecore is heated to the desired temperature, the heating plates are forcedor urged toward each other, thereby subjecting the core to compressionalong an axis substantially parallel to the thickness of the core. Thiscompression results is reducing the thickness of the core by 30% orless, preferably in the range of about 3% or about 5% to about 25% or30%. After this compression, the compressed core is allowed to cool tobelow, for example, slightly below, the glass transition temperature ofthe core material before the force on the plates is released.Conveniently, the compressed core is cooled to room temperature, e.g.,about 20° C. to about 25° C., before the force is released. The cooled,compressed core, which has an increased tensile strength relative to theuncompressed core, is now ready to be processed or formed into an IOL,such as IOL 10.

In one useful embodiment, only that portion or portions of theuncompressed material, for example, the uncompressed core, from whichthe haptic or haptics of the IOL are to be made are subjected tocompression, as described herein. This can be accomplished by usingheating plates designed to exert the desired compressive force on theoutside ring of the core, while exerting little or no compressive forceon the central region of the core, from which the optic of the IOL isformed. Preferably, the compressive force is applied so that the coreexpands outwardly away from the central region and not inwardly towardthe central region. One advantage of this embodiment is that the tensilestrength and/or other physical property or properties of the haptic orhaptics of the IOL are enhanced while the optic of the IOL is affected,for example, distorted, to a reduced extent, if at all, by thecompressive force.

The compressed core, which is thicker and larger in all dimensions thanthe IOL to be made therefrom, may be processed in accordance withconventional IOL forming techniques to produce an integral IOL, such asIOL 10. To illustrate, the compressed PMMA core can be formed into abi-convex single piece IOL by a process including the following steps:

(1) making a posterior cut on the compressed core;

(2) milling the compressed core;

(3) making an anterior cut on the compressed core; and

(4) polishing and cleaning the processed core.

The final IOL can be wrapped, for example, individually wrapped, andstored prior to being used.

It has been found that the controlled, limited compression employed inaccordance with the present invention results in a compressed core whichcan be formed into an IOL, for example, using conventional IOLmanufacturing techniques such as those described herein, at least aseffectively and efficiently as forming an IOL from the uncompressed coreusing the same IOL manufacturing techniques.

The use of the material processed as described herein, provides IOLswith fixation members which have enhanced tensile strength, flexibilityand fatigue resistance.

The following non-limiting examples illustrate certain aspects of thepresent invention.

EXAMPLES 1 TO 9

A series of compressed cores were prepared and tested for physicalproperties. Each of these compressed cores was made from aPMMA-containing material sold by ICI, Ltd. under the trademark Perspex®CQ-UV. Each of the uncompressed cores was 0.1 inch in thickness and hada diameter of about 0.7 inch.

Each of the cores was compressed as follows. The uncompressed core wasplaced between heating plates on the platen of a press. The core wassituated so that the heating plates were separated by the thickness ofthe uncompressed core. The heating plates were energized so as to heatthe uncompressed core to the desired temperature. After this hadoccurred, the press was activated so as to apply a compressive force tothe core and reduce the thickness by the desired amount. After this hadoccurred, and with the press still situated to apply force to thecompressed core, the compressed core was cooled to room temperature.Afterwards, the compressed core was removed from the press and subjectedto various stress/strain measurements at peak load and at ultimatestress.

Results of these tests are shown in Table I.

                  TABLE 1                                                         ______________________________________                                        At Peak Load        At Ultimate Stress                                        Load,      Stress,  Strain  Load, Stress,                                                                             Strain                                lb.        lb/in.sup.2                                                                            %       lb.   lb/in.sup.2                                                                         %                                     ______________________________________                                        Control 36.5   10,418   6.0   18.2  5,175 6.1                                 80° C.                                                                         31.0   10,055   6.0   13.9  4,500 6.1                                 (.010).sup.(1)                                                                80° C.                                                                         29.8   11,790   6.3   19.8  7,853 6.6                                 (.020).sup.(1)                                                                105° C.                                                                        38.2   11,863   7.4   19.9  6,171 7.5                                 (.030).sup.(1)                                                                105° C.                                                                        40.4   12,525   9.3   25.1  7,792 40.6                                (.010).sup.(1)                                                                105° C.                                                                        35.1   10,882   7.0   14.3  4,429 18.3                                (.020).sup.(1)                                                                105° C.                                                                        34.7   10,761   6.1   16.2  5,019 6.1                                 (.030).sup.(1)                                                                120° C.                                                                        46.9   13,406   10.2  23.0  6,574 41.4                                (.010).sup.(1)                                                                120° C.                                                                        41.2   12,780   8.6   25.9  8,047 19.3                                (.020).sup.(1)                                                                120° C.                                                                        41.5   11,843   8.5   21.4  6,097 17.4                                (.030).sup.(1)                                                                ______________________________________                                         .sup.(1) This number represents the amount of inches that the thickness o     the original core was reduced.                                           

These results indicate that the compressed cores tested generally haveenhanced tensile strength and enhanced resistance to stress and strainrelative to the uncompressed (Control) core. A relatively small numberof the compressed cores tested exhibit no such enhancements. The resultspresented in Table 1 are based on a single core tested at each set ofconditions. This, together with the inherent variability of the testprocedure employed, are considered to be the two major reasons forcertain of the compressed cores exhibiting no property enhancements.Under more controlled or less variable conditions, significantlyenhanced tensile strength and resistance to stress and strain, relativeto uncompressed cores, should occur throughout the range of testconditions noted in Table 1.

EXAMPLE 10

A number of cores having compositions similar to those described inExample 1, were compressed, as described in Example 1, at a temperatureof 120° C. so as to reduce the thickness of the uncompressed core by10%. These compressed cores, along with a number of uncompressed cores,were conventionally formed into intraocular lenses, similar inconfiguration to IOL 10, as shown in the drawings.

These lenses were subjected to a reverse bending test to determine thestrength of the haptics of such IOLs.

The results of these reverse bending tests indicated that the haptics ofthe IOLs made from the compressed cores broke on the average upon theapplication of a force equal to 164 g. The haptics of the IOLs made fromthe uncompressed cores broke on the average upon the application of aforce equal to 12 g. This substantial improvement in haptic bendingstrength, more than 1250% improvement, is clear evidence that thepresent controlled and limited compression processing results in IOLshaving very beneficial physical properties, such as tensile strength andflexibility, which are very much enhanced as a result of thiscompression processing.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. An intraocular lens comprising:an optic; and atleast one fixation member integral with and extending from said optic,said optic and said at least one fixation member being made from acompressed item having a compressed thickness, said compressed itemcomprising a polymer selected from the group consisting of methylmethacrylate homopolymers, methyl methacrylate-containing copolymers andmixtures thereof, said compressed item being derived by subjecting anitem which comprises said polymer and which has a thickness tocompression along a single axis substantially parallel to said thicknessto reduce said thickness, provided that said at least one fixationmember has a reverse bend strength of at least about 164 g.
 2. Theintraocular lens of claim 1 wherein said thickness is reduced by 30% orless.
 3. The intraocular lens of claim 1 which is the only intraocularlens formed from said compressed item.
 4. The intraocular lens of claim1 wherein said subjecting occurs at a temperature in the range of about80° C. to about 130° C.
 5. The intraocular lens of claim 1 wherein saidsubjecting said item to compression results in substantially noadditional polymerization or curing of said polymer.
 6. The intraocularlens of claim 1 wherein said at least one fixation member has increasedflexibility as a result of subjecting said item to compression relativeto a fixation member made from an identical item which is not sosubjected to compression.
 7. The intraocular lens of claim 1 whichcomprises two of said fixation members each of which has a very smallcross section and a free end away from said optic so that the overallsize of said intraocular lens between said free ends of said fixationmembers is in the range of about 9 mm to about 14 mm.
 8. The intraocularlens of claim 1 wherein said at least one fixation member has a reversebend strength which is increased by about 1250% or more relative to afixation member made from an identical item which is not so subjected tocompression.
 9. An intraocular lens comprising:an optic; and at leastone fixation member integral with and extending from said optic, said atleast one fixation member being made from a compressed item having athickness, said compressed item comprising a polymer selected from thegroup consisting of methyl methacrylate homopolymers, methylmethacrylate-containing copolymers and mixtures thereof, said compresseditem being derived by subjecting an item which comprises said polymerand which has a thickness to compression to reduce said thickness,provided that said at least one fixation member has a reverse bendstrength which is increased by about 1250% or more relative to afixation member made from an identical item which is not so subjected tocompression.
 10. The intraocular lens of claim 9 wherein said thicknessis reduced by 30% or less.
 11. The intraocular lens of claim 10 whereinsaid at least one fixation member has increased flexibility as a resultof subjecting said item to compression relative to a fixation membermade from an identical item which is not so subjected to saidcompression.
 12. The intraocular lens of claim 9 wherein said at leastone fixation member is more uniform relative to a fixation member madefrom a stretched item formed by stretching an identical item along atleast two mutually angulated axes to increase tensile strength and saidsubjecting occurs along an axis substantially parallel to saidthickness.
 13. The intraocular lens of claim 9 which comprises two ofsaid fixation members each of which has a very small cross section and afree end away from said optic so that the overall size of saidintraocular lens between said free ends of said fixation members is inthe range of about 9 mm to about 14 mm.
 14. The intraocular lens ofclaim 9 wherein said subjecting said item to compression occurs at atemperature in the range of about 80° C. to about 130° C.
 15. Theintraocular lens of claim 9 wherein said at least one fixation memberhas increased flexibility as a result of said subjecting said item tocompression relative to a fixation member made from an identical itemwhich is not so subjected to compression.
 16. The intraocular lens ofclaim 9 wherein said subjecting said item to compression results insubstantially no additional polymerization or curing of said polymer.17. An intraocular lens comprising:an optic; and two fixation membersintegral with and extending from said optic, each of said fixationmembers having a very small cross section and a free end away from saidoptic so that the overall size of said intraocular lens between saidfree ends of said fixation members is in the range of about 9 mm toabout 14 mm, said optic and said fixation members being made from asingle item having a thickness and comprising a polymer selected fromthe group consisting of methyl methacrylate homopolymers, methylmethacrylate-containing copolymers and mixtures thereof, said item beingderived by subjecting an item which comprises said polymer and which hasa thickness to compression to reduce said thickness, provided that eachof said fixation members has a reverse bend strength of at least about164 g.
 18. The intraocular lens of claim 17 wherein said thickness isreduced by 30% or less, and said subjecting occurs along a single axissubstantially parallel to said thickness and at a temperature in therange of about 80° C. to about 130° C.
 19. The intraocular lens of claim17 which is the only intraocular lens formed from said compressed item,and each of said fixation members has a reverse bend strength which isincreased by about 1250% or more relative to a fixation member made froman identical item which is not subjected to compression.